A printing ink is generally formulated according to strict performance requirements demanded by the intended market application and required properties. Whether formulated for office printing or for production printing, a particular ink is expected to produce images that are robust and durable under stress conditions. In a typical design of a piezoelectric ink jet printing device, the image is applied by jetting appropriately colored inks during four to six rotations (incremental movements) of a substrate (an image receiving member or intermediate transfer member) with respect to the ink jetting head, i.e., there is a small transaction of the printhead with respect to the substrate in between each rotation. This approach simplifies the printhead design, and the small movements ensure good droplet registration. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops.
Pigments are a class of colorants useful in a variety of applications such as for example paints, plastics and inks, including inkjet printing inks. Dyes have typically been the colorants of choice for inkjet printing inks because they are readily soluble colorants and, more importantly, do not hinder the reliable jetting of the ink. Dyes have also offered superior and brilliant color quality with an expansive color gamut for inks, when compared with conventional pigments. However, because dyes are molecularly dissolved in the ink vehicle, they are often susceptible to unwanted interactions that lead to poor ink performance, for example photooxidation from light (will lead to poor lightfastness), dye diffusion from the ink into paper or other substrates (will lead to poor image quality and showthrough), and the ability for the dye to leach into another solvent that makes contact with the image (will lead to poor water/solventfastness). In certain situations, pigments are the better alternative as colorants for inkjet printing inks since they are insoluble and cannot be molecularly dissolved within the ink matrix, and therefore do not experience colorant diffusion. Pigments can also be significantly less expensive than dyes, and so are attractive colorants for use in all printing inks.
Key issues with using pigments for inkjet inks are their large particle sizes and wide particle size distribution, the combination of which can pose critical problems with reliable jetting of the ink (i.e. inkjet nozzles are easily blocked). Pigments are rarely obtained in the form of single crystal particles, but rather as large aggregates of crystals and with wide distribution of aggregate sizes. The color characteristics of the pigment aggregate can vary widely depending on the aggregate size and crystal morphology. Thus, an ideal colorant that is widely applicable in, for example, inks and toners, is one that possesses the best properties of both dyes and pigments, namely: 1) superior coloristic properties (large color gamut, brilliance, hues, vivid color); 2) color stability and durability (thermal, light, chemical and air-stable colorants); 3) minimal or no colorant migration; 4) processable colorants (easy to disperse and stabilize in a matrix); and 5) inexpensive material cost. Thus, there is a need addressed by embodiments of the present invention, for smaller nanos-sized pigment particles that minimize or avoid the problems associated with conventional larger-sized pigment particles. There further remains a need for processes for making and using such improved nano-sized pigment particles as colorant materials. The present nanosized pigment particles are useful in, for example, paints, coatings and inks (e.g., inkjet printing inks) and other compositions where pigments can be used such as plastics, optoelectronic imaging components, photographic components, and cosmetics among others. The following documents provide background information:
U.S. Pat. No. 6,902,613 discloses a mixture of an organic nanosize pigment comprising of from 50 to 99% by weight of the nanosize pigment and 1 to 50% by weight based of a low molecular weight naphthalene sulfonic acid formaldehyde polymer and its use as a particle growth and crystal phase director for the preparation of a direct pigmentary organic pigment or in pigment finishing.
WO 2004/048482 discloses a mixture of an organic nanosize pigment comprising of from 50 to 99% by weight of the nanosize pigment and 1 to 50% by weight based of a low molecular weight polysulfonated hydrocarbon, in particular naphthalene mono- or disulfonic acid formaldehyde polymer, and its use as a particle growth and crystal phase director for the preparation of a direct pigmentary organic pigment or in pigment finishing.
U.S. patent application Publication No. 2006/0063873 discloses a process for preparing nano water paint comprising the steps of: A. modifying the chemical property on the surface of nano particles by hydroxylation for forming hydroxyl groups at high density on the surface of the nano particles; B. forming self-assembly monolayers of low surface energy compounds on the nano particles by substituting the self-assembly monolayers for the hydroxyl groups on the nano particles for disintegrating the clusters of nano particles and for forming the self-assembly monolayers homogeneously on the surface of the nano particles; and C. blending or mixing the nano particles having self-assembly monolayers formed thereon with organic paint to form nano water paint.
U.S. patent applicaton Publication No. 2005/0109240 describes a method of producing a fine particle of an organic pigment, containing the steps of: flowing a solution of an organic pigment dissolved in an alkaline or acidic aqueous medium, through a channel which provides a laminar flow; and changing a pH of the solution in the course of the laminar flow.
U.S. Pat. No. 3,201,402 discloses a process for the production of pigment dyestuffs of the quinacridone-7,14-dione series, which consists of reaction 1 more of 2,5-dihalogenoterephthalic acid and one or more of its esters either simultaneously or successively with 2 moles of an aromatic amine or of a mixture of different aromatic amines, in which at least one position ortho to the amino group is free, and coverting the resulting 2,5-diarylaminoterephthalic acid or its ester into a quinacridone-7,14-dione by heating at a high temperature in an acid condensation medium, if desired in presence of an inert organic solvent.
Kento Ujiiye-Ishii et al., “Mass-Production of Pigment Nanocrystals by the Reprecipitation Method and their Encapsulation,” Molecular Crystals and Liquid Crystals, v. 445, p. 177 (2006) describes that quinacridone nanocrystals with controlled size and morphology were readily fabricated by using a pump as an injection apparatus of the reprecipitation method for mass-production and injecting concentrated N-methyl-2-pyrrolidinone solution. The reference describes that encapsulation of quinacridone nanocrystals using polymer was achieved and quite improved dispersibility was confirmed for the encapsulated nanocrystals.
Hideki Maeta et al., “New Synthetic Method of Organic Pigment Nano Particle by Micro Reactor System,” in an abstract available on the internet, describes a new synthetic method of an organic pigment nano particle was realized by micro reactor. A flowing solution of an organic pigment, which dissolved in an alkaline aqueous organic solvent, mixed with a precipitation medium in a micro channel. Two types of micro reactor can be applied efficiently on this build-up procedure without blockage of the channel. The clear dispersion was extremely stable and had narrow size distribution, which were the features, difficult to realize by the conventional pulverizing method (breakdown procedure). These results proved the effectiveness of this process on micro reactor system.
WO 2006/132443 A1 describes a method of producing organic pigment fine particles by allowing two or more solutions, at least one of which is an organic pigment solution in which an organic pigment is dissolved, to flow through a microchannel, the organic pigment solution flows through the microchannel in a non-laminar state. Accordingly, the contact area of solutions per unit time can be increased and the length of diffusion mixing can be shortened, and thus instantaneous mixing of solutions becomes possible. As a result, nanometer-scale monodisperse organic pigment fine particles can be produced in a stable manner.
K. Balakrishnan et al., “Effect of Side-Chain Substituents on Self-Assembly of Perylene Diimide Molecules: Morphology Control,” J. Am. Chem. Soc., vol. 128, p. 7390-98 (2006) describes the use of covalently-linked aliphatic side-chain substiutents that were functionalized onto perylene diimide molecules so as to modulate the self-assembly of molecules and generate distinct nanoparticle morphologies (nano-belts to nano-spheres), which in turn impacted the electronic properties of the material. The side-chain substituents studied were linear dodecyl chain, and a long branched nonyldecyl chain, the latter substituent leading to the more compact, spherical nanoparticle.
WO 2006/011467 discloses a pigment, which is used, for example, in color image display devices and can form a blue pixel capable of providing a high level of bright saturation, particularly a refined pigment, which has bright hue and is excellent in pigment properties such as lightfastness, solvent resistance and heat resistance, and a process for producing the same, a pigment dispersion using the pigment, and an ink for a color filter. The pigment is a subphthalocyanine pigment that is prepared by converting subphthalocyanine of the specified formula, to a pigment, has diffraction peaks at least at diffraction angles (2θ) 7.0°, 12.3°, 20.4° and 23.4° in X-ray diffraction and an average particle diameter of 120 to 20 nm.
WO 2006/005536 discloses a method for producing nanoparticles, in particular, pigment particles. Said method consists of the following steps: (i) a raw substance is passed into the gas phase, (ii) particles are produced by cooling or reacting the gaseous raw substance and (iii) an electrical charge is applied to the particles during the production of the particles in step (ii), in a device for producing nanoparticles. The disclosure further relates to a device for producing nanoparticles, comprising a supply line, which is used to transport the gas flow into the device, a particle producing and charging area in order to produce and charge nanoparticles at essentially the same time, and an evacuation line which is used to transport the charged nanoparticles from the particle producing and charging area.
Japanese Patent Application Publication No. JP 2005238342 A2 discloses irradiating ultrashort pulsed laser to organic bulk crystals dispersed in poor solvents to induce ablation by nonlinear absorption for crushing the crystals and recovering the resulting dispersions of scattered particles. The particles with average size approximately 10 nm are obtained without dispersants or grinding agents for contamination prevention and are suitable for pigments, pharmaceuticals, etc.
WO 2004026967 discloses nanoparticles manufactured by dissolving organic pigments in organic solvents containing at least 50 vol. % amides and adding the organic solvent solutions in solvents, which are poor solvents for the pigments and comparable with the organic solvents, while stirring. Thus, quinacridone pigment was dissolved in 1-methyl-2-pyrrolidinone and added to water with stirring to give a fine particle with average crystal size 20 nm.
U.S. Pat. No. 6,837,918 discloses a process and apparatus that collects pigment nanoparticles by forming a vapor of a pigment that is solid at room temperature, the vapor of the pigment being provided in an inert gaseous carrying medium. At least some of the pigment is solidified within the gaseous stream. The gaseous stream and pigment material is moved in a gaseous carrying environment into or through a dry mechanical pumping system. While the particles are within the dry mechanical pumping system or after the nanoparticles have moved through the dry pumping system, the pigment material and nanoparticles are contacted with an inert liquid collecting medium.
U.S. Pat. No. 6,537,364 discloses a process for the fine division of pigments which comprises dissolving coarsely crystalline crude pigments in a solvent and precipitating them with a liquid precipitation medium by spraying the pigment solution and the precipitation medium through nozzles to a point of conjoint collision in a reactor chamber enclosed by a housing in a microjet reactor, a gas or an evaporating liquid being passed into the reactor chamber through an opening in the housing for the purpose of maintaining a gas atmosphere in the reactor chamber, and the resulting pigment suspension and the gas or the evaporated liquid being removed from the reactor through a further opening in the housing by means of overpressure on the gas entry side or underpressure on the product and gas exit side.
U.S. Pat. No. 5,679,138 discloses a process for making ink jet inks, comprising the steps of: (A) providing an organic pigment dispersion containing a pigment, a carrier for the pigment and a dispersant; (B) mixing the pigment dispersion with rigid milling media having an average particle size less than 100 μm; (C) introducing the mixture of step (B) into a high speed mill; (D) milling the mixture from step (C) until a pigment particle size distribution is obtained wherein 90% by weight of the pigment particles have a size less than 100 nanometers (nm); (E) separating the milling media from the mixture milled in step (D); and (F) diluting the mixture from step (E) to obtain an ink jet link having a pigment concentration suitable for ink jet printers.
Japanese Patent Application Publications Nos. JP 2007023168 and JP 2007023169 discloses providing a pigment dispersion compound excellent in dispersibility and flowability used for the color filter which has high contrast and weatherability. The solution of the organic material, for example, the organic pigment, dissolved in a good solvent under the existence of alkali soluble binder (A) which has an acidic group, and a poor solvent which makes the phase change to the solvent are mixed. The pigment nanoparticles dispersed compound re-decentralized in the organic solvent containing the alkali soluble binder (B) which concentrates the organic pigment nanoparticles which formed the organic pigment as the particles of particle size less than 1 μm, and further has the acidic group.
Kazuyuki Hayashi et al., “Uniformed nano-downsizing of organic pigments through core-shell structuring,” Journal of Materials Chemistry, 17(6), 527-530 (2007) discloses that mechanical dry milling of organic pigments in the presence of mono-dispersed silica nanoparticles gave core-shell hybrid pigments with uniform size and shape reflecting those of the inorganic particles, in striking contrast to conventional milling as a breakdown process, which results in limited size reduction and wide size distribution.
U.S. Patent Application Publication No. 2007/0012221 describes a method of producing an organic pigment dispersion liquid, which has the steps of: providing an alkaline or acidic solution with an organic pigment dissolved therein and an aqueous medium, wherein a polymerizable compound is contained in at least one of the organic pigment solution and the aqueous medium; mixing the organic pigment solution and the aqueous medium; and thereby forming the pigment as fine particles; then polymerizing the polymerizable compound to form a polymer immobile from the pigment fine particles.
Other publications of interest, and other aspects of which may be selected for embodiments of the present disclosure, include:    1) Herbst, K. Hunger, Industrial Organic Pigments, “Quinacridone Pigments” Wiley-VCH Third Edition, p. 452-472 (2004);    2) F. Kehrer, “Neuere Entwicklung auf den Gebiet der Chemie organischer Pigmentfarbstoffe,” Chimia, vol. 28(4), p. 173-183 (1974);    3) B. R. Hsieh et al, “Organic Pigment Nanoparticle Thin Film Devices via Lewis Acid Pigment Solublization and In Situ Pigment Dispersions,” Journal of Imaging Science and Technology, vol. 45(1), p. 37-42 (2001);    4) Swiss Patent No. 372316 to H. Bohler et al, Nov. 30, 1963; and    5) Swiss Patent No. 404034 to H. Bohler, Jun. 30, 1966
The appropriate components and process aspects of each of the foregoing may be selected for the present disclosure in embodiments thereof, and the entire disclosure of the above-mentioned references are totally incorporated herein by reference.